Grazing: The Spatial Dimension

Landscapes are not uniform in time or space.  Estimated stocking rates tend to be conservative, and on the low side, often in attempt to account for sites that are susceptible to deterioration and overgrazing.  But these conservative estimates and a laissez-faire approach to grazing management are counter-productive, especially to land managers looking to manage for and balance a number of different landscape variables. Research in southern African grasslands has shown that landscapes are comprised of a “mosaic of patches representing palatable and unpalatable grass species.”  Stocking rate recommendations suggest a uniform landscape that does not conform to a “one size fits all” approach.  Often, this can result in further deterioration of a complex managed landscape. Other research has sought to measure the effects of adequate recovery on these landscape patches.  These researchers postulate that “the differential use of preferred areas in the landscape results in uneven distribution of animal impact, and periods of below average precipitation compound the effects of herbivory, providing periods of accelerated deterioration.” This research, conducted under drought conditions, concluded that weather effects, particularly precipitation, predominantly determine changes in herbaceous basal area.  Measurements of comparisons between rotational and continuous grazing demonstrated that “although rotational grazing did not prevent deterioration in basal area and bare ground with the series of four drought years, it did decrease the rate of deterioration.” The patch effect of animal grazing has been documented elsewhere.  In this research, data was collected on cattle gains, cattle activity, distance traveled and forage utilization.  Three treatments were compared: one time-controlled rotation of eight 24-ha paddocks, one continuously grazed treatment of two 24-ha paddocks, and continuous grazing on one 207-ha paddock.  Utilization decreased dramatically at distances greater than 3 km from water on the 207-ha paddock, and at distances greater of 1.0 to 1.6 km on the 24-ha paddock. Anthropogenic landscape deterioration, therefore, is often a result of poor spatial distribution of grazing livestock.  Key management decisions like the placement of watering points, grazing system, and stocking rates interact with the natural variability of climate to determine the successional trajectory, nutrient cycles, and productivity of heterogeneous landscape patches.  The ability to control grazing duration, repetition, and patch recovery, along with the ability to distribute animals evenly across the landscape, can alleviate the stresses caused to sensitive areas on the landscape and reduce patch deterioration. Kellner, K., and O.J.H. Bosch, 1992. Influence of patch formation in determining stocking rate for southern African grasslands. Journal of Arid Environments. Vol. 22 No. 1, 99-105 pp. Teague, W.R., S.L. Dowhower, and J.A. Waggoner.,2004. Drought and grazing patch dynamics under different grazing management. Journal of Arid Environments. Vol. 58 97-117 pp. Hart, R.H., S. Clapp, and P.S.Test. 1993. Grazing strategies, stocking rates, and frequency and intensity of grazing on western wheatgrass and blue grama. Journal of Range Management. Vol. 46. No. 2, 122-126 pp.